Contact structure for an electric circuit breaker



March 18,1969 L. L.BAIRD ET AL 3,433,915

CONTACT STRUCTURE FOR AN ELECTRIC CIRCUIT BREAKER Filed July 19, 1967 .Sheet IN VE N TORS L M mm A M Li 5 Ml E LMM A R ATTORNEY M r 18, 1969 L. BAIRD ET AL 3,433,915-

CONTACT STRUCTURE FOR AN ELECTRIC CIRCUIT BREAKER Filed July 19, 1967 .Shet v 2 of 2 air ATTORNEY United States Patent 4 Claims ABSTRACT OF THE DISCLOSURE An electric circuit breaker comprising a pivotallymounted contact arm and a link connected to the contact arm for driving it between open and closed positions. At its free end, the contact arm has a butt contact and a separate slide contact. The contact arm and the link are mounted on separate universal-type joints that permit the contact arm and the link to rock together about an axis connecting the centers of the two universal joints, thereby permitting a parallel relationship to be developed between the slide contact and a complementary slide contact while the butt contact remains in engagement with a complementary butt contact.

Background of the invention This invention rleates to contact structure for an electric circuit breaker and, more particularly, relates to contact structure of the general type disclosed and claimed in US. Patent 3,249,729--Fornwalt, assigned to the assignee of the present invention.

In the contact structure of the Fornwalt patent, there is a movable contact member comprising two closelyspaced, ivotally-mounted contact arms that are simultaneously moved in generally-parallel, spaced-apart planes. These contact arms have transverse butt contact surfaces that abut against complementary butt contact surfaces when moved into closed position. In a position between said parallel planes, there is a stationary protuberance having slide contact surfaces substantially parallel to said parallel planes. The contact arms also have slide surfaces generally parallel to those on said protuberance but normally spaced therefrom.

When the movable contact member is driven closed, the butt contacts first engage, and this initiates the flow of current therethrough. If this current rises to a high value, high electromagnetic forces of attraction will be developed between the closely-spaced contact arms; and these forces drive the contact arms together, causing the normally-separated slide surfaces to engage under high pressure. This shunts a portion of the high current through the slide contact surfaces, reducing the arcing duty on the butt contacts.

In order for the slide surfaces to make good contact under these conditions, it is important that free movement of the contact member be permitted in directions that permit a generally parallel relationship to be developed between the slide surfaces.

Summary An object of our invention is to provide a mechanism for driving the movable contact arms that is able to perform its driving function without interfering with free motion of the contact arms into positions where the desired parallel relationship between the sliding contact surfaces is developed.

Another object is to provide a mechanism of this type which includes means for adjusting the normal spacing between the complementary sliding surfaces without interfering with the desired free motion of the contact arms.

In carrying out our invention in one form, we provide a driving shaft to which contact closing force is applied. For transmitting this closing force to the contact arms, a pair of connecting links are mounted on the shaft and are pivotally connected at their opposite end to the contact arms. The contact arms are mounted on a stationary support by means of universal joints, and the connecting links are mounted on the driving shaft by means of universal joints. These universal joints permit each connecting link and the contact arm to which it is connected to rock about an axis that interconnects the axis of the driving shaft and the pivot axis of the contact arms. This rocking movement allows the desired parallel relationship to be developed between the complementary slide surfaces.

Brief description of drawings For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a side elevational view partly in section showing contact structure embodying one form of the invention.

FIG. 2 is an end view of the contact structure as seen from the right hand side of FIG. 1.

FIG. 3 is a sectional view along the line 33 of FIG. 1.

FIG. 4 is a sectional view along the line 4-4 of FIG. 1.

FIG. 5 is a sectional view along the line 55 of FIG. 1.

FIG. 6 is a sectional view along the line 6-6 of FIG. 1.

FIG. 7 is an enlarged sectional view along the line 77 of FIG. 1, taken when the contact structure is in the closed position.

Description of preferred embodiment Referring now to FIGS. 1 and 2, the circuit breaker comprises a base 11, relatively stationary contact structure 12 mounted on the base, and an electroconductive bracket 13 mounted on the base in spaced relationship to the stationary contact structure. A movable contact member 14 is supported by bracket 13 for pivotal movement about an axis 16. When the movable contact member 14 is pivoted counterclockwise from its position of FIG. 1, its upper portion is moved into circuit-making engagement with the stationary contact structure 12, as will soon be described in greater detail. After the contacts have been thus engaged, pivotal movement in the opposite direction will separate the movable contact 14 from the stationary contact structure 12 to interrupt the circuit.

The components 12, 1G and 14 constitute the contact structure of one pole unit of the circuit breaker, and other similar pole units -(not shown) can be mounted for gang operation on the base member 11 adjacent to the illustrated pole unit.

The stationary contact structure 12 comprises a vertically extending conductive stud 18 suitably secured to base 11. Projecting from stud 18 at vertically-spaced locations are contact-supporting lugs 19 best seen in FIGS. 5 and 6. Each of these lugs 19 is divided into two horizontally-diverging branches 19a and 19b. Pivotally supported on the outer end of each of these branches is a contact finger 20. The outer end of each branch has a generally cylindrical bearing surface 21 which provides a fulcrum for contact fingers supported thereon, and the pivotal connection between each finger and lug forms a current-carrying joint.

As can be seen in FIGS. 5 and '6, the contact fingers 20 are arranged in pairs and are all electrically interconnected by virtue of the common conductive stud 18. The fingers of these pairs are respectively supported on opposite bearing surfaces in opposed relationship to each other, with the opposed fingers of each pair being pivotally movable in a common horizontal plane. The opposing or inner ends of the contact fingers 20 of each pair move in separate relatively short arcuate paths. The opposed ends of the fingers are respectively provided with generally fiat, complementary butt contact surfaces 25 generally disposed in a common vertical plane, as viewed in FIGS. 6 and 5.

The inner end of each contact finger 20 has an extension 26 disposed to engage a common stop 27, as seen in FIGS. and 6, for determining the limit of the arcuate movement of tne contact surface in one direction. The outer end 28 of each contact finger has a tension spring 29 connected thereto for establishing a biasing torque on the contact finger that tends to move contact surface 25 along an arcuate path in a forward direction away from base 11. As seen in FIGS. 5 and 6, such movement of the finger is limited by stop 27. This arrangement permits relatively limited deflection or yielding of each contact finger in a rearward direction.

The movable contact structure 14 comprises a pair of electrically-parallel arms 38 and 40 respectively provided with butt contact surfaces 43 and 4317. During circuit-closing movement, the arms 38 and 40 and their respective butt contact surfaces 43 and 43b move in vertically-spaced parallel planes disposed approximately perpendicular to the planes defined by the parallel arcuate paths of the contact surfaces of each set of adjacent fingers 20. When the butt contact surfaces 43 on the moving arms engage the butt contact surfaces 25 on the fingers 20 at the end of a circuit-closing operation, each contact finger is pivoted on its fulcrum 21 against the biasing torque of spring 29. In this manner, the usual contact-wiping action is obtained between the mating contacts 20 and 43, 43b.

The illustrated stationary contact assembly 12 comprises a first group of stationary contacts, referred to hereinafter as intermediate contacts, and a second group of stationary contacts located beneath the first group and referred to hereinafter as primary current-carrying contacts. The intermediate contacts, which are illustrated in FIG. 5, are designated 12a, and the primary current-carrying contacts, which are illustrated in FIG. 6, are designated 12!). The stationary intermediate contacts 12a and the stationary primary contacts 12b are of generally the same configuration but are so arranged that engagement with r the movable contact member 14 during circuit-closing occurs first at the intermediate contacts 12a and then at the primary current-carrying contacts 12b. FIG. 5 depicts the intermediate contacts 12a when initial engagement is made, while FIG. 6 shows the primary currentcarrying contacts 12b, 43b at the same instant still slightly separated. On opening, separation occurs first at the primary current-carrying contacts 12b and then at the intermediate contacts 12a. The surface on movable contact 14 which engages the primary current-carrying contacts is designated 43b. The primary current-carrying contacts and the intermediate contacts cooperate in a conventional manner so that arcing duty is borne primarily by the intermediate contacts, and current-carrying duty is borne primarily by the primary current-carrying contacts.

The two arms 38 and which constitute the movable contact member are pivotally mounted on bracket 13 by the ball or universal joint shown in detail in FIG. 3. Referring to FIG. 3, it will be seen that bracket 13 comprises two side-by-side lugs 48, each of which is formed with a socket of a partially spherical form at its outer side. These lugs 48 are fixed to base 11. Each of the contact arms 38 and 40 is formed with an embossment 52 having an external surface 54 of partially spherical form fitting within the socket 50 of an adjacent lug. This balland-socket type mounting permits universal movement of the contact arm.

For maintaining the generally spherical surfaces of the ball-and-socket joints in high pressure contact with each other as the contact arms 38 and 40 are moved, a pair of compression springs 55 are provided at the outer sides of the contact arms. These compression springs 55 are mounted about a transverse pin 56 that extends freely through registering openings 59 and 60 in the contact arms and lugs. Nuts 62 suitably threaded on opposite ends of pin 56 provide reaction points against which the outer ends of compression springs 55 act. Suitable washers 64 are disposed between the inner ends of springs 55 and the contact arms to transmit spring force to the contact arms. Thus, springs 55 exert a lateral force on the contact arms 38, 40 that hold the generally spherical embossments thereon in high pressure engagement with the mating surfaces of socket 50, maintaining this high pressure through all movement of the contact arms. This continuously-maintained, high-pressure engagement between these surfaces permits high currents to be transmitted through these ball joints without harmful arcing. This spring force is supplemented by an electrodynamic force whenever the arms 38 and 40 are conducting current. Since the parallel arms pass current in the same direction, a magnetic force of attraction is established tending to reduce the spacing between the contact arms, whereby additional contact pressure is exerted at the contiguous slide surfaces 50, 54.

During circuit-closing and circuit-opening movement, arms 38 and 40, which constitute the movable contact member 14, are caused to move together about pivot axis 16 by the actuating mechanism 15 of FIG. 4, which will soon be described. The upper ends of the two contact arms 38 and 40 are biased apart by a compression spring 70, best shown in FIG. 4.

For increasing the current-handling capabilities of the illustrated circuit breaker, we utilize the arcing contact structure shown and claimed in the aforesaid US. Patent 3,249,729Fornwalt. This arcing contact structure comprises at the free end of the respective contact arms 38 and 40 special contact tips 74 and 76 of arc-resistant metal. (See FIGS. 2 and 7.) Tips 74 and 76, which move in parallel, spaced-apart joint relationship during opening and closing movement, respectively carry slide contact surfaces 75 and 77 generally parallel to their planes of movement. The slide surfaces 75 and 77 are disposed facing one another, and so long as the movable contact members open, the spring between the contact arms will yieldably maintain a predetermined spacing between surfaces and 77.

Cooperating with these contact tips 74, 76 is a protuberance 78 forming a pair of the stationary contact structure and mounted above finger contacts 20. Referring to FIG. 2, protuberance 78 is disposed on a bisector of the opposing contact fingers, and therefore it projects centrally between contact tips 74 and 76 of arms 38 and 40 when the movable contact member 14 is closed. Protuberance 78 is suitably electrically connected to stud .18 in parallel with fingers 20.

Protuberance 78 is made of suitable are resistant material, and it has a pair of parallel slide contact surfaces 81 and 83 on opposite sides thereof. Whenver the contact surfaces 25 of the intermediate contact fingers 20 are engaged by the associated contact surfaces 43 carried by parallel arms 38 and 40 the slide surfaces 81 and 83 of protuberance 78 are respectively adjacent the facing sliding surfaces 75 and 77 on contact tips 74 and 76 of the arms. Slide contact surface 81 is therefore adapted to be separably engaged by sliding contact surface 75, and slide contact surface 83 is adapted to be separably engaged by slide contact surface 77. These cooperating contact surfaces, however, remain separated and will not touch each other on movement of contact member 14 to its closed-circuit position until after the butt contact surfaces 25, 43 conduct more than a predetermined amount of current. This follows from the fact that the breadth of protuberance 78 is smaller than the spacing between slide surfaces 75 and 77 when no current is being conducted. Thus, the arms 38 and 40 must be moved laterally toward one another in order to effect interengagement of adjacent sliding contact surfaces. Such lateral movement of arms 38 and 40 is effected by the electrodynamic forces of attraction acting on them in response to their parallel conduction of current above a predetermined value. This predetermined value is many times full load current but is substantially less than the currents expected under short circuit conditions. Thus, under short circuit conditions, slide contact surfaces 75 and 77 move into engagement with slide contact surfaces 81 and 83, respectively, thereby shunting the interengaged contact means 43, 25. Subsequent opening movement of movable contact member 14 results in the intermediate contact surfaces 43 and 25 being disengaged before the now-engaged slide contact surfaces separate. Hence, the slide contact surfaces are the last opened, and any arcing that occurs will occur between contact tips 74, 76 and protuberance 78.

For preventing excessive deflection of the contact arms 38 and 40 under the influence of the electromagnetic forces of attraction, a suitable projecting stop 86 is provided on one of the contact arms to engage the other contact arm after a predetermined amount of movement together occurs in this region.

For transmitting closing motion to the movable contact arms 38 and 40, a toggle-type closing mechanism is relied upon. Referring to FIGS. 1, 2 and 4, this toggle mechanism comprises a first set of identical spaced-apart toggle links 91 and a second set of identical spaced-apart toggle links 93, the two sets of toggle links 91 and 93 being pivotally interconnected at one end by a shaft 94 best seen in FIG. 4. Each of the toggle links 91 is pivotally supported at its opposite end on base 11 by a stationary pivot pin 92. Each toggle link 93 is pivotally connected at its opposite end to one of the movable contact arms '38 or 40 by a pivot pin 95. Referring to FIG. 4, pivot pin 95 is suitably fixed to toggle link 93, but relative rotary motion is permitted between pin 95 and the contact arm 38 or 40.

Closing motion is transmitted to the toggle mechanism 15 through a vertically-extending operating rod 97 suitably connected to toggle link 91. When operating rod 97 is driven upwardly as viewed in FIG. 1, it pivots the toggle link 91 in a counterclockwise direction about pivot 92; and this motion is transmitted to movable contact member 14 through the other toggle links 93, causing movable contact 14 to pivot counterclockwise about its stationary axi 16. Near the end of the closing stroke, the toggle linkage 15 approaches an on-center condition in which the line interconnecting pivots 92 and 94 closely approaches the axis of pivot 95, thereby developing especially high contact-closing forces for overcoming any short-circuit-produced opposing forces that might then be developed.

For backing up the toggle links 93 so as to prevent any further separation thereof than is shown in FIG. 4, a pair of spaced-apart back-up members 99 are provided. Each back-up member 99 is mounted at one end on shaft 94 and at its other end has a slot 101 that freely receives the pivot pin 95. As shown in FIG. 4, each back-up member 99 has a hub 100 surrounding shaft 94 on which the associated toggle member 93 is mounted.

The position of these back-up members 99 on shaft 94 is determined by a pair of adjusting bushings 102 which respectively bear against the rear surfaces of backup members 99. Each adjusting bushing 102 is threaded into one of the toggle links 91. Since the spacing between toggle links 91 is fixed (-by suitable means not shown), it will be apparent that adjustment of bushings 102 with respect to toggle links 91 determines the spacing between 6 the adjusting bushings. A suitable lock nut 104 threaded on each adjusting bushing 102 locks the adjusting bushing in any desired position on the toggle link 91. A compression spring 106 located between the toggle links 93 urges these toggle links 93 apart along shaft 94, but the maximum spacing developed between toggle links 93 is limited by the back-up members 99 to the distance determined by adjusting bushings 102 bearing against the rear surfaces of back-up members 99.

For reasons soon to be explained, each of the toggle links 93 is mounted on shaft 94, or more specifically on concentric hub 100, by means of a universal joint 110. Each universal joint 110 comprises a partially spherical section 112 pressed on to hub and fitting into the bore 113 of toggle link 93. This bore is made large enough to permit the toggle link 93 to rotate in any direction about the center 115 of the spherical section 110. A cylindrical spacer sleeve 116 pressed into the bore 113 prevents axial shifting of spherical section 112 on hub 100. The spacer sleeve 116 has an enlarged central opening that has substantial clearance with respect to hub 100, thus permitting a substantial amount of rotary motion of toggle link 93 about the center 115 without interference from the hub.

The universal joints between toggle links 93 and shaft 94 permit the toggle links 93 to rock about centers 115 when the contact arms 38 and 40 are moved toward each other. As previously pointed out, when closing takes place against high currents, the contact arms 38 and 40 are driven toward each other by the electromagnetic forces of attraction developed by the high currents, and this carries their outer tips 74 and 76 into engagement with protuberance 78. To permit the slide surfaces 75, 77 on the contact tips to make good engagement with the slide surfaces 81, 83 on the protuberance, it is important that the contact arms 38 and 40 be free to rock on the ball joints 50, 54 of FIG. 3. For preventing the driving toggle links 93 from interfering with this rocking movement of contact arms 38 and 40, we rely upon the universal joints of FIG. 4. These universal joints 110 permit the toggle links 93 to freely rock about centers in response to rocking of the contact arms 38 and 40, thus preventing any interference with the desired motion of the contact arms. The slots 101 in the backup member 99 permit this rocking motion of the toggle links 93 and contact arms 38 and 40 to occur without any interference from the back-up members.

The above-described rocking of contact arm 38 and its associated toggle link 93 can be looked upon as a rocking movement of the contact arm and toggle link about a reference axis that interconnects the pivot axis 16 of the contact member 38 and the axis of driving shaft 94. This reference axis, which is depicted at 117 in FIG. 1, passes through the center of the two ball points 50, 52 and 110. The contact arm 40 and its associated toggle link rock about another reference axis (not shown) parallel to reference axis 117 and passing through the center of the other two ball joints 50, 52 and 110.

For adjusting the spacing between slide surfaces 75 and 81 and between slide surfaces 77 and 83 (FIG. 2), we rely upon the adjusting bushings 102 of FIG. 4. Adjusting these bushings with respect to the toggle links 91 in which they are mounted produces a change in the spacing between the other toggle links 93; and this, in turn, changes the spacing between contact arms 38 and 40 (in view of the connection 95, 101 between the toggle links and the contact arms). The adjusting bushings 102 can be individually adjusted to change the spacing between one set of sliding contact surfaces 75, 81 independently of the other, 77, 83. If the adjusting bushings 102 are adjusted in a direction to separate them, springs 106 and 70 cause the contact members 38 and 40 to separate from each other.

While We have shown and described a particular embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects; and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric circuit breaker,

(a) a base member,

(b) relatively stationary contact structure mounted on said base member and including (i) butt contact surfaces and (ii) a protuberant part having substantially parallel slide contact surfaces on opposite sides thereof disposed transversely of said butt contact surfaces,

(c) a bracket mounted on the base member in spaced relationship to said stationary contact structure,

(d) a pair of electrically-parallel contact arms pivotally connected to said bracket and having free ends respectively disposed for arcuate movement in planes transversely disposed with respect to said butt contact surfaces, the arms having in the vicinity of their respective free ends (i) transverse contact surfaces arranged to engage said butt contact surfaces respectively and (ii) additional slide contact surfaces facing one another and disposed respectively adjacent to the opposite slide surfaces of said protuberant part whenever said transverse contact surfaces are in engagement with the respective butt contact surfaces,

(c) said arms being movable toward each other at their free ends when the current through the arms exceeds a predetermined value, thereby forcing the slide surfaces on said arms into pressure engagement with the slide surfaces on said protuberant part,

(f) actuating means coupled to said arms for jointly moving the transverse contact surfaces thereof into and out of engagement with said butt contact surfaces,

(g) said actuating means comprising a shaft spaced from said axis of rotation and a pair of links, each having one end mounted on said shaft and an opposite end connected to one of said contact arms at a location spaced from said axis of rotation, and

(h) the mounting of each link on. said shaft and the pivotal connection of each contact arm on said bracket being universal-type joints that permit said arm and its associated link to rock about a reference axis interconnecting said axis of rotation and the axis of said shaft.

2. A circuit breaker as defined in claim 1 and further comprising:

(a) a pair of adjusting members on said shaft mounted for movement into different positions of adjustment therealong,

(b) said adjusting members serving as stops for limiting the maximum spacing of said links on said shaft,

(c) and spring means for forcing said links apart into positions determined by said adjusting members.

3. A circuit breaker as defined in claim 1 and further comprising:

(a) a pair of adjusting members on said shaft mounted for movement into different positions of adjustment therealong,

(b) said adjusting members serving as stops for limiting the maximum spacing of said links on said shaft,

(c) back-up members respectively mounted on said shaft between said adjusting members and said links,

(d) said back-up members respectively extending between said shaft and the connections between said links and said contact arm,

(e) pivot pins connecting said contact arms to said connecting links and extending freely through slots in said back-up members, and

(f) spring means forcing said links apart against said backup members into positions determined by said adjusting members.

4. In an electric circuit breaker,

(a) a base member,

(-b) relatively stationary contact structure mounted on said base member and including (i) butt contact surfaces and (ii) a protuberant part having substantially parallel slide contact surfaces on opposite sides thereof disposed transversely of said butt contact surfaces,

(c) a bracket mounted on the base member in spaced relationship to said stationary contact structure,

(d) a pair of electrically-parallel contact arms pivotally connected to said bracket and having free ends respectively disposed for arcuate movement in planes transversely disposed with respect to said butt contact surfaces, the arms having in the vicinity of their respective free ends (i) transverse contact surfaces arranged to engage said butt contact surfaces, respectively, and

(ii) additional slide contact surfaces facing one another and disposed respectively adjacent to the opposite slide surfaces of said protuberant part whenever said transverse contact surfaces are in engagement with the respective butt contact surfaces,

(e) said arms being movable toward each other at their free ends when the current through the arms exceeds a predetermined value, thereby forcing the slide surfaces on said arms into pressure engagement with the complementary slide surfaces on said protuberant P (f) actuating means coupled to said arms for jointly moving the transverse contact surfaces thereof into and out of engagement with said butt contact surfaces,

(g) said actuating means comprising a shaft spaced from said axis of rotation and a pair of links, each having one end mounted on said shaft and an opposite end connected to one of said contact arms at a location spaced from said axis of rotation, and

(h) means for forcing each of said contact arms to rock without interference from said shaft about a reference axis so located that a substantially parallel relationship is developed between the complementary slide surfaces when the free ends of said arms move toward each other.

References Cited UNITED STATES PATENTS 2,938,986 5/1960 Baskerville et a1. 200164 2,962,573 11/1960 Scully 200 3,033,964 5/ 1952 Titus. 3,249,729 5/ 1966 Fornwalt.

ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner.

US. Cl. X.R. 

